1. Field of the Invention
The present invention relates to a process for preparing an aqueous solution comprising ferric chloride. The ferric chloride is produced from the chlorination of titanium-bearing materials.
2. Description of the Related Art
Large amounts of metal chlorides arise as by-products from various industrial processes. For example, in a chloride process for making titanium dioxide (TiO.sub.2) pigment, titanium-bearing material or ore is chlorinated to produce titanium tetrachloride (TiCl.sub.4) and other metal chloride by-products. The metal chloride by-products are highly acidic and often contain iron chlorides as a major ingredient. Many processes to treat these materials are expensive and produce a product that must be disposed of by neutralization, landfilling, deepwelling, or other disposal methods.
The need therefore exists for a process for treating aqueous media containing metal chlorides that provides non-hazardous products that can be used in commercial applications.
It is known that iron chloride can be used as a flocculant for treatment of waste water. Conventionally high purity iron chloride solutions have been utilized for this purpose. Tedious and expensive processes have been developed to purify metal chloride by-product streams to render them suitable for use to treat wastewater.
Cairns and Kleinfelder, U.S. Pat. No. 3,261,664 describe a process to remove ferrous chloride (FeCl.sub.2) from hot gases containing ferric chloride (FeCl.sub.3), TiCl.sub.4, and blowover solids comprising unreacted ores and carbon-containing material from a reaction for the chlorination of titanium-bearing materials which involves the following steps: (a) passing a stream containing FeCl.sub.2, FeCl.sub.3 and TiCl.sub.4 into a flue at 900.degree. C.; (b) injecting cool TiCl.sub.4 into the flue to cool the stream to 500-550.degree. C. which condenses FeCl.sub.2 as a solid; (c) passing the mixture containing solid FeCl.sub.2 and remaining gases to a dust or cyclone-type separator to separate solid FeCl.sub.2 and blowover solids from the gases; (d) passing the gases to cooling towers, wherein FeCl.sub.3 is removed by conventional means, e. g., by cooling the gases to 250-270.degree. C. by a shower of an inert cooling medium such as cool TiCl.sub.4, to form solid FeCl.sub.3 ; (e) passing the mixture containing gases and solid FeCl.sub.3 to a cyclone separator to remove solid FeCl.sub.3 ; (f) condensing the remaining gases which are now free of solid chlorides; and (g) recovering liquid TiCl.sub.4.
Rado and Nelson, U.S. Pat. No. 3,906,077 disclose a process for recovering substantially pure FeCl.sub.3 from chlorinating an iron-containing ore which includes separation of a major portion of non-volatile solids in a first cyclone, followed by a cooling step (addition of liquid TiCl.sub.4), to precipitate FeCl.sub.3, use of a second cyclone to separate FeCl.sub.3 and all other remaining non-volatile solids, and purification of FeCl.sub.3 by recovery as overhead from a treatment zone at 350-700.degree. C.
Hartmann and Schmeir, U.S. Pat. No. 5,248,497 disclose a process for the recovery of ferrous chloride from the gaseous effluent resulting from chlorination of titanium-containing material which involves: (a) separating FeCl.sub.2 and blowover solids (unreacted coke, ore) and other metal chlorides in a cyclone to form cyclone dust; (b) slurrying the cyclone dust with a liquid (water, HCl); (c) removing the water-insoluble constituents of the slurry e.g., by filtration; (d) evaporating the solution under vacuum; (e) cooling the evaporated solution to allow FeCl.sub.2 to crystallize; and (f) separating the FeCl.sub.2 crystals. This patent does not describe a process for separating FeCl.sub.3 or a process to provide a solution of FeCl.sub.3 having low solids content.
Heretofore, a process where titanium-containing material is chlorinated to produce a metal chloride vapor stream which is cooled to a temperature greater than 500.degree. C. to condense out a fraction of the FeCl.sub.2 and other metal chlorides having high boiling points such as lead chloride (PbCl.sub.2), manganese chloride (MnCl.sub.2), magnesium chloride (MgCl.sub.2), and chromium chloride (CrCl.sub.3) in a cyclone separator has been commercially practiced. The precipitated solids as well as most of the entrained coke, ore, and gangue solids are collected in the cyclone underflow, thus purifying the FeCl.sub.3 vapor stream which exits in the cyclone overflow.
In this commercial process, the cyclone overflow is further cooled to 180-240.degree. C., wherein FeCl.sub.3 is precipitated and then slurried with water to form an aqueous solution of FeCl.sub.3 containing dissolved FeCl.sub.2 and other miscellaneous metal chlorides, and trace amounts of water-insoluble coke, ore, and gangue solids. The FeCl.sub.3 solution is further processed through a screening/settling process to reduce solids concentration to provide a product suitable for wastewater treatment applications.
Although the above-described process is effective in producing an aqueous solution of FeCl.sub.3, it would be desirable to have an improved process which removes a larger fraction of the chlorides having high boiling point temperatures from the FeCl.sub.3 stream. Also, when the above-described process is operated, solids build up on downstream piping and equipment causing restrictions and pluggage. Thus, it would be desirable to have a process which could be run more continuously with fewer downstream restrictions and pluggage.
The present invention provides an improved process which can be operated more continuously with fewer pluggage and restriction problems. The resulting aqueous solution has a high iron content, particularly a high FeCl.sub.3 content, while having a low chromium chloride content, which is advantageous in wastewater treatment applications.